Microcystin Elimination During Sediment Contact

Abstract

Microcystins (MCYSTs) are a group of structurally similar toxic peptides produced by cyanobacteria ("blue-green algae") which occur frequently in surface waters worldwide. Reliable elimination is necessary when using these waters as drinking water sources. Bank filtration and artificial groundwater recharge utilize adsorption and degradation processes in the subsurface, commonly through sand and gravel aquifers, for the elimination of a wide range of substances during drinking water (pre-) treatment. To obtain parameters for estimating whether MCYST breakthrough is likely in field settings, we tested MCYST elimination in laboratory experiments (batch experiments, column experiments) under a range of conditions. Adsorption coefficients (k(d)-values) obtained from batch studies ranged from 0.2 mL/g for filter sand to 11.6 mL/g for fine grained aquifer materials with 2% fine grains (<63 microm) and 0.8% organic matter. First order degradation rates in column studies reached 1.87 d(-1) under aerobic conditions and showed high variations under anoxic conditions (<0.01-1.35 d(-1)). These results show that, next to sediment texture, redox conditions play an important role for MCYST elimination during sediment passage. Biodegradation was identified as the dominating process for MCYST elimination in sandy aquifer material.

Discerning biodegradation and adsorption of microcystin-LR in a shallow semi-enclosed bay and bacterial community shifts in response to associated process

“…Yet, very few studies have discriminated the dual pathways (biodegradation and adsorption) for MCs removal within natural solid medium (i.e., sand or sediment). One example (Grützmacher et al, 2010) used autoclaved sand as the filter media to discern adsorption and biodegradation roles in MCs elimination. It is notable that autoclaving may alter the inherent adsorption ability of non-sterile solid media by destroying textural properties (e.g., organic matter), hence the adsorption fraction of non-sterile media might not be truly reflected.…”

Mechanisms and Factors Affecting Sorption of Microcystins onto Natural Sediments

“…This specific property of MC-RR cause it to (1) increase propensity to form cation bridging (resulting from the additional positive protonated arginine cation) and enhance its sorption affinity to cation-exchange sites present on both OM and clay and (2) provide additional binding sites and tend to form more hydrogen bonds with sediment components (OM and/or clay). Gr€ utzmacher et al 19 also attributed the higher sorption capacity of MC-RR in sediments to the higher acidity constant of arginine (pK a value 12.5) for MC-RR, compared with leucine for MC-LR (pK a value 9.7). Furthermore, the logK ow values of MC-LR (-0.37) and MC-RR (-1.09) under neutral condition, which were measured in our laboratory according to De Maadg et al, 20 indicate that both MCs are hydrophilic and thus hydrophobic interactions are unlikely to play a major role in MCs sorption onto sediment considering so much lower logK ow values.…”

Microcystins, nutrient dynamics, and other environmental factors during blooms of non-microcystin-producingAphanizomenon flos-aquaein Upper Klamath Lake, Oregon, 2009

“…Although high dissolved microcystin concentrations in the water column may promote direct adsorption onto bottom sediments, microcystin adsorption may be limited in shallow systems (Grützmacher et al 2010). In Upper Klamath Lake, a strong negative correlation was observed between microcystin concentrations and site depth in surficial sediment samples from randomly selected sites (Table 2).…”